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WELL LOGGING
&
PETROPHYSICAL ANALYSIS
PRESENTED BY:
Irfan MUHAMMAD
HISTORY
HISTORY
• Wireline logging or wireline coring, as it was known then, was born in 1929
• Two mining engineers, Conrad and Marcel Schlumberger, extended surface
measurement techniques for finding ore bodies into the well bore.
• The process they used involved making electrical resistance measurements
from two copper stakes driven into the surface.
• The resistance was made between them
HISTORY
HISTORY
HISTORY
HISTORY
HISTORY
HISTORY
FIRST ELOG
HISTORY
HISTORY
 In the mid-1930’s Schlumberger dominated the market
 In 1936 Dr. Blau (Humble Oil) developed single cable logging
system.
 In 1936, encouraged by a number of major oil companies,
Halliburton enters logging business.
 In 1937 Halliburton signed an agreement with Humble Oil, to use Dr.
Blau’s patents.
 Schlumberger sued and wins case in Houston courts.
 Halliburton appeals to the federal courts and wins
 Schlumberger decides not to appeal to the supreme court.
 In 1938, Halliburton begins commercial caliper logging.
 In 1939, Halliburton developed the “Russian Gun” for export.
1930s
 Halliburton cement and stimulating business continues to
grow.
 Halliburton develop FM logging system.
 FM system featured SP and three resistivity curves.
 First commercial logs run in 1949
HISTORY
1940s
1950s
• The first guard log introduced (1950)
• Entered radiation logging business through a license with the Texas Company
• Logging trucks of the period were four wheel drive, painted red and silver.
• Approached Paul Charrin of PGAC, in hopes of penetrating the logging
market in 1955.
• Purchased Welex for $28,000,000
HISTORY
1950s (continued)
• Welex became surviving logging unit after the merger, 1957
1960s
• In 1961, Welex facility in Forth Worth was closed
1970s
• In the fall of 1977 Halliburton began an aggressive plan to improve logging
training and technology.
• W.D.M. Smith was recruited from Dresser Atlas in Canada
• Multi-conductor cable and digital data transmission introduced.
HISTORY
1980s
• 1988, Halliburton buys Gearhart
1990s
• 1997, Halliburton buys Numar
THE BOREHOLE ENVIRONMENT
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WHAT IS INVASION?
 Process by which mud filtrate is forced into
permeable formations, and the solid particles
of the mud are deposited on the borehole
wall where they form a mudcake.
 Due to pressure difference between mud
column and formation pressure.
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BEFORE INVASION
18 BTC
DURING INVASION
19 BTC
AFTER INVASION
20 BTC
MUD FILTRATE INVASION
Porosity = 30 %
Porosity = 10 %
Porosity = 20 %
mud filtrate
mud filtrate
mud filtrate
mud cake
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INVASION MODEL
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NO INVASION - SHALE
Resistivity
Depth of Investigation
Virgin
10 60 90
Known condition:
Curves overlay indicating no
invasion, impermeable
SHALLOW INVASION - WATER ZONE (RMF >RW)
Depth of Investigation
Virgin
10 60 90
Known condition:
Curves separate indicating
invasion profile
Mud cake occurs
with invasion
Rmc >Rmf
Resistivity
SHALLOW INVASION - OIL ZONE
Step Invasion
Resistivity
Depth of Investigation
Virgin
10 60 90
TRANSITION ZONE - OIL ZONE
Resistivity
Depth of Investigation
Virgin
Flushed
10 60 90
TRANSITION - WATER ZONE (RMF > RW)
Resistivity
Depth of Investigation
Virgin
Flushed
10 60 90
ANNULUS INVASION - OIL ZONE
Resistivity
Depth of Investigation
Virgin
Ann.
Flushed
10 60 90
LOG EXAMPLE
GAMMA RAY LOG
GAMMA RAY LOG
THEORY OF MEASUREMENT
There are two types of Gamma Ray measurements used by the wireline logging
industry.
Naturally occurring Gamma Rays:
 These are Gamma Rays that occur naturally in the formation and have relatively low
energy levels
 Tools that measure natural Gamma Rays are known as standard and gamma
spectrometry tools.
 Standard Gamma Ray tools measure the occurrence of all Gamma Rays.
Spectrometry Gamma Ray tools determines the concentrations of the three normally
present radioactive elements namely
i. Uranium (Ur235/238)
ii. Potassium (Isotope 19K40)
iii. Thorium (Th232).
Induced Gamma Rays:
Tools such as gamma - gamma logs use a high energy Gamma Ray source to
measure other formation parameters.
GAMMA RAY LOG
GAMMA RAY LOG
How are Gamma Ray's measured?
Typically two types of Gamma Ray detectors have been used in the industry, the
Geiger Mueller and Scintillation crystals counter.
The Geiger Mueller is more reliable and robust but the Scintillation is more accurate.
When a Gamma Ray strikes the crystal a single photon of energy is emitted. A burst of
electrons are then emitted as the photon hits the photocathode. The electrons multiply
as they hit several anodes in an electric field until a small electric pulse is produced.
Each electric pulse is produced from a single detected gamma ray
Gamma Rays occur naturally and at random as bursts of energy over time.
To reduce statistical variation in the Gamma Ray measurement, logging companies
take an average reading over time. The recommended time constant is 2 seconds
The slower the logging speed the more accurate the measurement
GAMMA RAY LOG
GAMMA RAY LOG
APPLICATION
Standard Gamma Ray Applications:
• Primary depth reference for all logging runs
• Correlation from well to well
• Lithology identification
• Identification of organic material, permeable beds and source rocks
• Fracture identification
• Calculate clay volumes
• Mineral analysis
Natural Gamma Ray Tool (NGT) Applications:
• Detect, identify and evaluate radioactive minerals
• Identify clay type and calculate clay volumes
• Provides insight into depositional environment and the diagenetic history
• Uranium response of NGT is sometimes useful as a moved fluid indicator
• Permeable beds may have higher Uranium salt content than less permeable
beds.
GAMMA RAY LOG
Presentation
 The Gamma Ray is presented in track 1 by a thin continuous line with the
mnemonic GR or a variation of this. Typically a scale from 0 to 200 with units
of API. The right scale can be reduced to 150 or 120 if Gamma Ray activity is
low.
Alternatively Spectrometry Gamma Ray tools can also present the following
curves: -
1. Total Gamma Ray (SGR)
2. Uranium free Gamma Ray (CGR) - to distinguish permeable streaks with
high Uranium.
3. Ratio Th/K - to distinguish between minerals
4. Ratio Th/U - to distinguish between minerals
GAMMA RAY LOG
SPONTANEOUS POTENTIAL
LOG
SPONTANEOUS POTENTIAL LOG
HISTORY
 One of the first log measurements made.
 It was discovered as a potential that effected old electric logs.
 It has been in use for over the past 50 years.
THEORY OF MEASUREMENT
 An electrode (usually lead) is lowered down the well and an electrical
potential is registered at different points in the hole with respect to surface
electrode.
 The SP is a recording of the difference in potential of a moveable electrode in
a borehole and a fixed electrode on the surface.
 In order to record a potential the hole must contain conductive mud, as it
cannot be recorded in air or oil-base mud.
 Logging rate is approximately 1500m per hour and recordings are continuous
 SP results from electric currents flowing in the drilling mud. There are three
sources of the currents, two electrochemical and one electrokinetic.
SPONTANEOUS POTENTIAL LOG
SPONTANEOUS POTENTIAL LOG
 Deflection of SP is caused by the Electrochemical Ec and Electrokinetic Ek
actions
Electrochemical Component
Ec = Elj + Em
 These two effects are the main components of the SP. They are caused as a
result of differing salinities in the mud filtrate and the formation water.
Elj: "Liquid Junction Potential"
 The ions Na+ and Cl- have different mobilities at the junction of the invaded
and virgin zones. The movement of the ions across this boundary generates a
current flow and hence a potential.
 If the salinity of the mud in the borehole is weaker or stronger than that of the
formation water the potential generated between the two solutions is known as
the Liquid Junction Potential or Elj. The greater the difference between the
salinity of the solutions the greater the potential.
SPONTANEOUS POTENTIAL LOG
 Em: "Membrane Potential"
Shale’s are permeable to Sodium ions but not to Chlorine ions. Hence there is
a movement of charged particles through the shale creating a current and thus
a potential. This is known as the membrane potential or Em.
Electrokinetic Component
 An Electrokinetic potential (Ek) is generated by the flow of mud filtrate through
a porous permeable bed.
 It depends upon the resistivity of the mud filtrate and will only become
important if there are high differential pressures across the formation.
 This process is not well understood and the effects are normally negligible in
permeable formations because the mud cake builds quickly and halts any
further invasion.
 In low porosity, low permeability formations, the mud cake builds slowly and
the Electrokinetic potential becomes predominate
SPONTANEOUS POTENTIAL LOG
SPONTANEOUS POTENTIAL LOG
SPONTANEOUS POTENTIAL LOG
Deflection of the SP curve
 The SP measurement is constant but jumps suddenly to another level
when crossing the boundary between two different formations.
 When Rmf > Rw The SP deflects to the left (-ve SP) found in permeable
formations filled with formation water
 When Rmf < Rw The SP deflects to the right (+ve SP) found in permeable
formation filled with formation water
 There is no deflection in non-permeable or shaly formations.
SPONTANEOUS POTENTIAL LOG
SPONTANEOUS POTENTIAL LOG
LIMITATIONS AND PRESENTATION
Limitations
 Borehole mud must be conductive.
 Formation water must be water bearing and conductive.
 A sequence of permeable and non-permeable zones must exist.
 Small deflection occurs if Rmf=Rw
 Not fully developed in front of thin beds
Presentation
 SP is presented in track 1 by a thin continuous line with the mnemonic of SP.
 SP is measured in MV (millivolts) and although there is no absolute scale, a
relative scale of 10 MV per small division and usually -80 to 20MV across track
1 is used.
SPONTANEOUS POTENTIAL LOG
NEUTRON LOG
NEUTRON LOG
THEORY OF MEASUREMENT
 An Am241Be source emits neutrons into the formation at approximately 4MeV.
(Plutonium Berilium sources are no longer used since they can be broken down
to create atomic weapons).
 After collisions with the formation, the neutron energy levels fall to between 0.1
and 10eV. These are known as epithermal neutrons.
 After further collisions neutron energy levels fall below 0.03eV and these are
termed thermal neutrons.
 By virtue of its similar mass to neutrons, Hydrogen more than any other element
in the formation slows down the neutrons dramatically.
 A useful analogy is a billiard ball interacting with a ping-pong ball. The billiard ball
only loses significant velocity when it hits another billiard ball not when it hits a
ping-pong ball.
 Hydrogen is primarily only present in water, oil and gas, the neutron tool gives a
direct measurement of the fluid in the pore space of clean formations.
 Two detectors, one short spaced and the other long spaced from the source are
used to eliminate some borehole effects and detect the number of neutrons
returning back to the tool. A low neutron return count indicates the presence of
hydrogen and therefore porosity
NEUTRON LOG
 Once the neutrons reach the thermal stage, they are ready to be
captured.
 The presence of strong neutron absorbers like Chlorine have a capture
cross section about 100 times that of Hydrogen at the thermal level.
 Thermal neutrons therefore need to be corrected for fluid salinity and
matrix capture cross section effects.
 Epithermal neutrons do not need to be corrected for capture effects but
only have one tenth of the population of thermal neutrons.
 Some neutron tools like the CNT-GA can detect both epithermal and
thermal neutrons giving two different porosity measurements.
 The standard CNT Tool measures only thermal neutrons.
NEUTRON LOG
NEUTRON LOG
NEUTRON LOG
APPLICATION
 The Neutron tool is used to determine primary formation porosity, often called
the pore space on the formation rock which is filled with water, oil or gas.
 Together with other tools like the density, the lithology and formation fluid type
can also be determined.
NEUTRON LOG
NEUTRON LOG
Presentation
 Presented in track 5 and 6 by a dashed line with the mnemonic NPHI and with
scales, 45% to –15% (or .45 to –0.15 p.u.-porosity units
Typical Log Readings
100% Limestone = 0%
100% Sandstone = -2%
100% Dolomite = 1%
Shale = 30-45%
NEUTRON LOG
DENSITY LOG
DENSITY LOG
THEORY OF MEASUREMENT
 A 1.5 Ci Cs137 chemical source bombards gamma rays at 662keV energy into
the formation.
 The high-energy gamma rays interact with the electrons of the formation by way
of Compton scattering and lose energy in the process.
 Other processes also occur namely photoelectric absorption and pair production,
although pair production only becomes significant at energies above 1MeV.
 A low number of gamma rays detected through Compton scattering will indicate
a high electron density.
 A spectral or litho density tool measures not only the bulk density but also a
photoelectric absorption index PEF.
DENSITY LOG
 The photoelectric effect occurs when the incident gamma ray of low energy
is absorbed by the electron and the electron is then ejected from the atom.
PEF = (Z/A)3.6
A=Atomic weight, Z=Atomic number (or # of hydrogen atoms)
 The photoelectric effect of absorbed gamma rays is directly related to the Z,
the number of electrons per atom, which is fixed for each element.
 Different values of the PE curve indicate different types of formation rock
being measured and are independent of formation porosity.
DENSITY LOG
DENSITY LOG
APPLICATION
 The density tool is used to determine formation density and estimate
formation porosity.
 Together with other tools like the Neutron, the lithology and formation fluid
type can also be determined.
 The density tool can distinguish between oil and gas in the pore space by
virtue of their different densities.
 Modern density tools also measure the photoelectric effect to help
distinguish between rock lithologies, recognize presence of heavy minerals,
fracture identification when barite is present and additional clay evaluation.
 In addition the density can be used to determine Vclay and to calculate
reflection coefficients to process synthetics.
DENSITY LOG
DENSITY LOG
Synthetic Processing
 The Density is used along with the Sonic velocity to compute Acoustic
impedance (I) by:-
I = Density(rho) * Velocity (V)
 The Reflection coefficient (R) at a bed boundary is then determined by:-
R = (I2 - I1) / (I2 + I1)
 The Reflection coefficient is then used to generate synthetic processing curves
that can match the exploration seismic
DENSITY LOG
PRESENTATION
 Presented in track 5 and 6 by a thin continuous line with the mnemonic RHOB.
 For sandstone scales, 1.90 to 2.90 with units of g/cc and neutron from 45% to –
15%.
 For limestone scales, 1.95 to 2.95 with units of g/cc and neutron from 45% to –
15%.
 The amount of density correction is presented in track 6 by a dashed line with
the mnemonic DRHO.
 DRHO scales are -0.25 to 0.25 with units of g/cc.
DENSITY LOG
DENSITY LOG
Using compatible limestone scales for density (1.95 RHOB 2.95) and neutron
curves (45% NPHI –15%) then:-
 In a clean wet limestone RHOB and NPHI curves will overlay.
 In a shale RHOB plots right of NPHI depending on the amount of shale present.
 In a gas limestone RHOB plots > 3pu left of NPHI
 In a clean wet sand RHOB plots 3pu left of NPHI
 In a dolomite RHOB plots right of NPHI
Using compatible sandstone scales for density (1.90 RHOB 2.90) and neutron
curves (45% NPHI –15%) then:-
 In a clean wet sand RHOB and NPHI curves will overlay.
 In a shale RHOB plots right of NPHI depending on the amount of shale present.
 In an oil sand RHOB plots 1-3pu left of NPHI
 In a gas sand RHOB plots > 3pu left of NPHI
DENSITY LOG
Mineral RHOB (g/cc) PEF
100% Limestone 2.71 5.09
100% Sandstone 2.65 1.81
100% Dolomite 2.85 3.05
Shale 2.2-2.7 3.36 (typically)
Anhydrite 2.92-2.98 5.05
Salt 2.06 4.65
Coal 1.68 0.18
Hydrogen -0.61
Carbon -0.29
Water 1 -0.02
Typical Log Readings
SONIC LOG
SONIC LOG
THEORY OF MEASUREMENT:
 Transmitter emits sound waves into the formation and measures the time taken
to detect at a receiver of known distance from the transmitter.
 The Sonic tool operates at 20 cycles per second as sounds similar to a
pedestrian crossing at a set of traffic lights.
 The first arrival is the compressional or 'p' waves, which travel adjacent to the
borehole
 It is this arrival that is used to measure the individual travel times T1, T2, T3, and
T4. Two receivers for each transmitter eliminates the borehole signal.
 The transit time DT is computed from these travel times as shown in the
equation below.
 This particular arrangement of sonic tool transmitters and receivers is known as
the standard BHC Sonic tool and compensates for borehole washouts and also
for tool tilting in real time while logging.
DTLOG = [(T1 - T2) + (T3 - T4)] / 2
SONIC LOG
 T1 and T3 travel times have a Tx-Rx spacing of 5 feet and T2 and T4 travel times
have a Tx-Rx spacing of 3 feet.
 This results in a DT of 2 feet and is also the vertical resolution of the tool. The
shear signal arrives next which usually has a slightly larger amplitude than the
compressional arrival, then mud arrivals and Stoneley waves.
 The various arrivals in the received sonic signal can be seen in Figure 1. Stoneley
waves are used to interpret the existence of fractures
SONIC LOG
SONIC LOG
APPLICATION:
• Porosity PHIS
• Volume of clay VS
• Lithology
• Time-depth relationship
• Reflection coefficients
• Mechanical properties
• VDL/CBL
 By combining sonic and Checkshot data we can calibrate down hole log data
with surface seismic data.
 Mechanical properties can be determined from the shear and compressional
waves, fracture identification from shear and Stoneley waves and permeability
indication from Stoneley waves
Presentation
 Presentation is usually 140-40 us/ft (or 500-100 us/m) across tracks 5 & 6
SONIC LOG
SONIC LOG
. Material Delta-T(us/ft)
Non Porous Anhydrite 50
Solids Calcite 49.7
. Dolomite 43.5
. Granite 50.7
. Gypsum 52.6
. Limestone 47.6
. Quartz 52.9
. Salt 66.6
. Steel 50
. Casing 57.0
Water Saturated Dolomites (5-20%) 50.0-66.6
Porous Rocks Limestone (5-20%) 54.0 - 76.9
. Sandstones (5-20%) 62.5 - 86.9
.
Sands (unconsolidated - 20-
35%)
86.9 - 111.1
. Shales 58.8 - 143.0
Liquids Water (pure) 208
. Water (100,000mg/L of NaCl) 192.3
. Water (200,000mg/L of NaCl) 181.8
. Petroleum 238.1
. Mud 189
Gases Hydrogen 235.3
. Methane 666.6
RESISTIVITY LOGS
RESISTIVITY LOGS
THEORY OF MEASUREMENT
 Most resistivity logs measure from 10 to 100 ft3 of material around the sonde,
however the micro-resistivity log measures only a few cubic inches of material
near the borehole wall.
 Resistance (R-Ohms) is related to current (I-Amps) and voltage (V-Volts)
according to Ohm’s law and is described by: -
V= IR
 Resistivity (R) can be defined as the property of a material that resists the flow of
electric current, and is the voltage required to pass one amp through a cube with
a one meter square face area.
 The unit of measurement is Ohm-meter2/meter (ohm m2/m or ohm m).
RESISTIVITY LOGS
 The Induction logging tool determines resistivity by measuring the formation
conductivity.
 The Induction tool induces and focuses an electromagnetic field into the
formation adjacent to the tool by generating an alternating current source in the
primary coil.
 This induced electromagnetic field will produce a measurable current and
potential in the receiver coil of the tool proportional to the formation conductivity.
 The primary and secondary windings of a common transformer are a simple
analogy.
 The measured voltage in the receiver coil is then used to determine the
formation conductivity and thus the formation resistivity.
 Conductivity is the inverse of resistivity (1/resistivity) and has the units of mho/m
RESISTIVITY - REVIEW
1 Volt
1 meter
- +
Resistivity
1 W-m2/m
LATERAL DEVICES
LATERAL DEVICES
INDUCTION PRINCIPLES
Alternating
Signal, I(wt)
~
Transmitter
Oscillating Transmitted
Magnetic Field, B(wt)
Induced
Formation
Current
J(wt) ≈
aE(wt)
Detected
Magnetic Field, B2(wt)
Received
Signal, I2(wt)
Receiver
Secondary Magnetic Field
(from induced formation
currents)
WHEN TO RUN INDUCTION
High Water
Resistivity, Rw
Medium Water
Resistivity, Rw
Low Water Resistivity,
Rw
High Mud
Resistivity, Rm
Normally OK for
induction logs, if
porosity > 8%
otherwise Rt may be
too high (over 250 W-
m)
Perfect for
induction logging.
Perfect for induction
logging.
Medium Mud
Resistivity, Rm
Normally OK for
induction logs if
porosity > 10%
Perfect for
induction logging.
Perfect for induction
logging.
Low Mud
Resistivity, Rm
Not advised. Borehole
signal will often be
larger than formation
signal
Acceptable for induction
logging if porosity > 6%
and hole diameter < 10
inches, otherwise
borehole signal may
overwhelm formation
signal
PETROPHYSICAL
ANALYSIS
PETROPHYSICAL ANALYSIS
STEP 1:
VOLUME OF SHALE:
1) From Gamma Ray Log:
Vshale_IGR = (GRlog-GRminimum) / (GRmaximum-GRminimum)
2) From SP Log:
Vshale_ISP = (SP-SPcln) / (SPshl-SPcln)
Clavier Shale Correction
Vshale= 1.7 - (3.38 - (Vshale_IGR+0.7)^2)^0.5
Steiber Shale Correction
Vshale = 0.5 * Vshale_IGR / (1.5 – Vshale_IGR)
PETROPHYSICAL ANALYSIS
STEP 2
Net To Gross Ratio (NTG):
NTG=1-Vshale
PETROPHYSICAL ANALYSIS
STEP 3:
Befrore moving to this step first of all we have to identify lithology , if we don’t have
the well tops, the formula used for that purpose is .
RHOMa = (RHOB - PHIA * RhoF) / (1 - PHIA)
Step 3 involves the calculation of porosity
Different porosity types which are estimated from well logs are as follows
1) Density porosity
2) Neutron porosity
3) Average porosity
4) Sonic porosity
5) Effective porosity
PETROPHYSICAL ANALYSIS
STEP 3.a.
DENSITY POROSITY:
DPHI = (RhoM - RHOB) / (RhoM - RhoF)
RhoM= density of matrix (constant values)
RhoF= density of fluid (on log header)
RHOB= Bulk Density ( density log values)
Sandstone 2.65
Limestone 2.71
Dolomite 2.87
Fresh Water 1.0
Salt Water (120kppm) 1.1
Oil 0.85
PETROPHYSICAL ANALYSIS
STEP 3.b:
Sonic porosity:
Øsonic = (∆tlog - ∆tma) / (∆tf -∆tma)
Øsonic = Sonic derived porosity
∆tma = Interval transit time of the matrix
∆tlog = Interval transit time of formation
∆tf = Interval transit time of the fluid in the well bore
(Fresh mud = 189; salt mud = 185)
PETROPHYSICAL ANALYSIS
Where a sonic log is used to determine porosity in unconsolidated sands, an
empirical compaction factor or Cp should be added to the Wyllie et al equation:
Øsonic= (1/Cp) x [(∆tlog - ∆tma) / (∆tf -∆tma)]
Øsonic = Sonic derived porosity
∆tma = Interval transit time of the matrix
∆tlog = Interval transit time of formation
∆tf = Interval transit time of the fluid in the well bore
(Fresh mud = 189; salt mud = 185)
Cp = Compaction factor
Cp = (∆tsh x C ) /100
∆tsh = Interval transit time for adjacent shale
C = Constant which is normally 1.0
Empirical corrections for hydrocarbon effect:
Øsonic x 0.7 (gas)
Øsonic x 0.9 (oil)
PETROPHYSICAL ANALYSIS
Lithology ∆tma(µsec/ft) commonly used
Sandstone 55.5 to 51.0
Limestone 47.6
Dolomite 43.5
Anhydrite 50.0
Salt 67.0
Shale 167.5 - 62
PETROPHYSICAL ANALYSIS
STEP 3.c:
Average Porosity:
Also called as Neutron-Density Porosity, Neutron-Sonic Porosity as well
ØN-D= √(ØN
2+ ØD
2/2)
Whenever N-D Porosity log records density porosity of less than 0.0, a common
value is anhydrite. The following formula should be used to determine the N-D
porosity:
ØN-D= (ØN
2+ ØD
2/2)
PETROPHYSICAL ANALYSIS
STEP 3.d:
Effective Porosity:
Effective porosity=NTG*Average Porosity
PETROPHYSICAL ANALYSIS
STEP 4:
Resistivity of Water (Rw):
To calculate Rw there are several methods some of which invlove the usage of
standard sclumberger plots, while there are other in which we use certain
standard equations.
All steps with equations are explained as follows with their sub steps as wells
PETROPHYSICAL ANALYSIS
STEP 4.a:
Rmf at 75°F=Rmf*(temp+6.77)/81.77
STEP 4.b:
K=60+(0.133*Tf)
Tf=Formation Temperature
To calculate formation temperature we have to perform following steps
TEMPERATURE GRADIENT CALCULATION:
m=y-c/x
y=bottom hole temperature(BHT)
X=total depth of well
C=surface temperature
FORMATION TEMPERATURE CALCULATION:
Tf=m*x+c
Here x= Formation Depth
PETROPHYSICAL ANALYSIS
STEP 4.c:
Rmfe/Rwe=10^(-SSP/K)
Rmfe/Rwe=Ratio of resisitivity of mud filtrate equvalent to resistivity of water
equivalent
K= from step 4.b.
SSP= static spontaneous potential
CALCULATION OF SSP:
 First take SP in shale zone (Zone where GR is high representative of thick shale
package)—Shale baseline
 Then note SP in clean zone (porous, where hole condition is OK, don’t go for
Overguaged zones)__Sand baseline
Example:
SPshale= -20mV SPsand= -30mV SSP=-10mV
SPshale= -30 SPsand= -20 SSp=+10mv
PETROPHYSICAL ANALYSIS
STEP 4.d:
if Rmf at 75°F<0.1 then use following formula
Rmfe=(146*Rmf-5)/(337*Rmf+77)
If Rmf at 75°F>0.1 then use following formula
Rmfe=0.85*Rmf
STEP 4.e:
Rwe=Rmfe/(Rmfe/Rwe)
Rwe=Resistivity of water equivalent
Rmfe= from step 4.d
Rmfe/Rwe= from step 4.c
PETROPHYSICAL ANALYSIS
STEP 4.f:
If Rwe <0.12 use following formula
Rw @ 75°F=(77*Rwe+5)/(146-377*Rwe)
If Rwe >0.12 use following formula
Rw @ 75°F =-[0.58-10^(0.69*Rwe-0.24) ]
STEP 4.g:
Rw @ formation temperature=(Rw @ 75°F *81.77)/(Tf+6.77)
PETROPHYSICAL ANALYSIS
99 BTC
STEP 5:
Calculation Of Sw:
lateral log deep
(LLD)
F=a/Ø m induction log
deep
a=1
m=2
n=2
PETROPHYSICAL ANALYSIS
STEP 6:
Calculation Of Sxo:
Induction Log
Shallow
STEP 7: micro
spherical focused log
Calculation of Moveable Hydrocarbons
given on the
log header
STEP 8:
Calculation of Bulk volume of water(BVW):
PETROPHYSICAL ANALYSIS
STEP 9:
Calculation of Bulk volume of Hydrocarbon or Hydrocarbon Pore
Volume(HCPV):
HCPV=Ø (1- Sw)
STEP 10:
Calculation of residual oil saturation:
ROS= 1 - Sxo
STEP 11:
Calculation of moveable oil saturation:
MOS= Sxo - Sw
PETROPHYSICAL ANALYSIS
STEP 12:
Calculation of Permeability:
Swirr=Saturation of water (irreducible)
Swirr= [a/(2000*NPHI m )] 0.5
PETROPHYSICAL ANALYSIS
STEP 13:
Reserves Calculation:
Oil in Barrels; Depth in Feet
BBL = 7758 * Acres * PHIA * (1 - Sw)*h*R.F*Shape factor
Gas in Mcfd; Depth in Feet
MCF = 43,560 * Acres * PHIA * (1 - Sw)*h*R.F*Shape factor
R.F=60-80% (gas), 20-30%(oil)

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well logging & petrophysical analysis.pptx

  • 3. HISTORY • Wireline logging or wireline coring, as it was known then, was born in 1929 • Two mining engineers, Conrad and Marcel Schlumberger, extended surface measurement techniques for finding ore bodies into the well bore. • The process they used involved making electrical resistance measurements from two copper stakes driven into the surface. • The resistance was made between them
  • 11. HISTORY  In the mid-1930’s Schlumberger dominated the market  In 1936 Dr. Blau (Humble Oil) developed single cable logging system.  In 1936, encouraged by a number of major oil companies, Halliburton enters logging business.  In 1937 Halliburton signed an agreement with Humble Oil, to use Dr. Blau’s patents.  Schlumberger sued and wins case in Houston courts.  Halliburton appeals to the federal courts and wins  Schlumberger decides not to appeal to the supreme court.  In 1938, Halliburton begins commercial caliper logging.  In 1939, Halliburton developed the “Russian Gun” for export. 1930s
  • 12.  Halliburton cement and stimulating business continues to grow.  Halliburton develop FM logging system.  FM system featured SP and three resistivity curves.  First commercial logs run in 1949 HISTORY 1940s 1950s • The first guard log introduced (1950) • Entered radiation logging business through a license with the Texas Company • Logging trucks of the period were four wheel drive, painted red and silver. • Approached Paul Charrin of PGAC, in hopes of penetrating the logging market in 1955. • Purchased Welex for $28,000,000
  • 13. HISTORY 1950s (continued) • Welex became surviving logging unit after the merger, 1957 1960s • In 1961, Welex facility in Forth Worth was closed 1970s • In the fall of 1977 Halliburton began an aggressive plan to improve logging training and technology. • W.D.M. Smith was recruited from Dresser Atlas in Canada • Multi-conductor cable and digital data transmission introduced.
  • 14. HISTORY 1980s • 1988, Halliburton buys Gearhart 1990s • 1997, Halliburton buys Numar
  • 16. 16 BTC WHAT IS INVASION?  Process by which mud filtrate is forced into permeable formations, and the solid particles of the mud are deposited on the borehole wall where they form a mudcake.  Due to pressure difference between mud column and formation pressure.
  • 20. 20 BTC MUD FILTRATE INVASION Porosity = 30 % Porosity = 10 % Porosity = 20 % mud filtrate mud filtrate mud filtrate mud cake
  • 22. 22 BTC NO INVASION - SHALE Resistivity Depth of Investigation Virgin 10 60 90 Known condition: Curves overlay indicating no invasion, impermeable
  • 23. SHALLOW INVASION - WATER ZONE (RMF >RW) Depth of Investigation Virgin 10 60 90 Known condition: Curves separate indicating invasion profile Mud cake occurs with invasion Rmc >Rmf Resistivity
  • 24. SHALLOW INVASION - OIL ZONE Step Invasion Resistivity Depth of Investigation Virgin 10 60 90
  • 25. TRANSITION ZONE - OIL ZONE Resistivity Depth of Investigation Virgin Flushed 10 60 90
  • 26. TRANSITION - WATER ZONE (RMF > RW) Resistivity Depth of Investigation Virgin Flushed 10 60 90
  • 27. ANNULUS INVASION - OIL ZONE Resistivity Depth of Investigation Virgin Ann. Flushed 10 60 90
  • 30. GAMMA RAY LOG THEORY OF MEASUREMENT There are two types of Gamma Ray measurements used by the wireline logging industry. Naturally occurring Gamma Rays:  These are Gamma Rays that occur naturally in the formation and have relatively low energy levels  Tools that measure natural Gamma Rays are known as standard and gamma spectrometry tools.  Standard Gamma Ray tools measure the occurrence of all Gamma Rays. Spectrometry Gamma Ray tools determines the concentrations of the three normally present radioactive elements namely i. Uranium (Ur235/238) ii. Potassium (Isotope 19K40) iii. Thorium (Th232). Induced Gamma Rays: Tools such as gamma - gamma logs use a high energy Gamma Ray source to measure other formation parameters.
  • 32. GAMMA RAY LOG How are Gamma Ray's measured? Typically two types of Gamma Ray detectors have been used in the industry, the Geiger Mueller and Scintillation crystals counter. The Geiger Mueller is more reliable and robust but the Scintillation is more accurate. When a Gamma Ray strikes the crystal a single photon of energy is emitted. A burst of electrons are then emitted as the photon hits the photocathode. The electrons multiply as they hit several anodes in an electric field until a small electric pulse is produced. Each electric pulse is produced from a single detected gamma ray Gamma Rays occur naturally and at random as bursts of energy over time. To reduce statistical variation in the Gamma Ray measurement, logging companies take an average reading over time. The recommended time constant is 2 seconds The slower the logging speed the more accurate the measurement
  • 34. GAMMA RAY LOG APPLICATION Standard Gamma Ray Applications: • Primary depth reference for all logging runs • Correlation from well to well • Lithology identification • Identification of organic material, permeable beds and source rocks • Fracture identification • Calculate clay volumes • Mineral analysis Natural Gamma Ray Tool (NGT) Applications: • Detect, identify and evaluate radioactive minerals • Identify clay type and calculate clay volumes • Provides insight into depositional environment and the diagenetic history • Uranium response of NGT is sometimes useful as a moved fluid indicator • Permeable beds may have higher Uranium salt content than less permeable beds.
  • 35. GAMMA RAY LOG Presentation  The Gamma Ray is presented in track 1 by a thin continuous line with the mnemonic GR or a variation of this. Typically a scale from 0 to 200 with units of API. The right scale can be reduced to 150 or 120 if Gamma Ray activity is low. Alternatively Spectrometry Gamma Ray tools can also present the following curves: - 1. Total Gamma Ray (SGR) 2. Uranium free Gamma Ray (CGR) - to distinguish permeable streaks with high Uranium. 3. Ratio Th/K - to distinguish between minerals 4. Ratio Th/U - to distinguish between minerals
  • 38. SPONTANEOUS POTENTIAL LOG HISTORY  One of the first log measurements made.  It was discovered as a potential that effected old electric logs.  It has been in use for over the past 50 years. THEORY OF MEASUREMENT  An electrode (usually lead) is lowered down the well and an electrical potential is registered at different points in the hole with respect to surface electrode.  The SP is a recording of the difference in potential of a moveable electrode in a borehole and a fixed electrode on the surface.  In order to record a potential the hole must contain conductive mud, as it cannot be recorded in air or oil-base mud.  Logging rate is approximately 1500m per hour and recordings are continuous  SP results from electric currents flowing in the drilling mud. There are three sources of the currents, two electrochemical and one electrokinetic.
  • 40. SPONTANEOUS POTENTIAL LOG  Deflection of SP is caused by the Electrochemical Ec and Electrokinetic Ek actions Electrochemical Component Ec = Elj + Em  These two effects are the main components of the SP. They are caused as a result of differing salinities in the mud filtrate and the formation water. Elj: "Liquid Junction Potential"  The ions Na+ and Cl- have different mobilities at the junction of the invaded and virgin zones. The movement of the ions across this boundary generates a current flow and hence a potential.  If the salinity of the mud in the borehole is weaker or stronger than that of the formation water the potential generated between the two solutions is known as the Liquid Junction Potential or Elj. The greater the difference between the salinity of the solutions the greater the potential.
  • 41. SPONTANEOUS POTENTIAL LOG  Em: "Membrane Potential" Shale’s are permeable to Sodium ions but not to Chlorine ions. Hence there is a movement of charged particles through the shale creating a current and thus a potential. This is known as the membrane potential or Em. Electrokinetic Component  An Electrokinetic potential (Ek) is generated by the flow of mud filtrate through a porous permeable bed.  It depends upon the resistivity of the mud filtrate and will only become important if there are high differential pressures across the formation.  This process is not well understood and the effects are normally negligible in permeable formations because the mud cake builds quickly and halts any further invasion.  In low porosity, low permeability formations, the mud cake builds slowly and the Electrokinetic potential becomes predominate
  • 44. SPONTANEOUS POTENTIAL LOG Deflection of the SP curve  The SP measurement is constant but jumps suddenly to another level when crossing the boundary between two different formations.  When Rmf > Rw The SP deflects to the left (-ve SP) found in permeable formations filled with formation water  When Rmf < Rw The SP deflects to the right (+ve SP) found in permeable formation filled with formation water  There is no deflection in non-permeable or shaly formations.
  • 46. SPONTANEOUS POTENTIAL LOG LIMITATIONS AND PRESENTATION Limitations  Borehole mud must be conductive.  Formation water must be water bearing and conductive.  A sequence of permeable and non-permeable zones must exist.  Small deflection occurs if Rmf=Rw  Not fully developed in front of thin beds Presentation  SP is presented in track 1 by a thin continuous line with the mnemonic of SP.  SP is measured in MV (millivolts) and although there is no absolute scale, a relative scale of 10 MV per small division and usually -80 to 20MV across track 1 is used.
  • 49. NEUTRON LOG THEORY OF MEASUREMENT  An Am241Be source emits neutrons into the formation at approximately 4MeV. (Plutonium Berilium sources are no longer used since they can be broken down to create atomic weapons).  After collisions with the formation, the neutron energy levels fall to between 0.1 and 10eV. These are known as epithermal neutrons.  After further collisions neutron energy levels fall below 0.03eV and these are termed thermal neutrons.  By virtue of its similar mass to neutrons, Hydrogen more than any other element in the formation slows down the neutrons dramatically.  A useful analogy is a billiard ball interacting with a ping-pong ball. The billiard ball only loses significant velocity when it hits another billiard ball not when it hits a ping-pong ball.  Hydrogen is primarily only present in water, oil and gas, the neutron tool gives a direct measurement of the fluid in the pore space of clean formations.  Two detectors, one short spaced and the other long spaced from the source are used to eliminate some borehole effects and detect the number of neutrons returning back to the tool. A low neutron return count indicates the presence of hydrogen and therefore porosity
  • 50. NEUTRON LOG  Once the neutrons reach the thermal stage, they are ready to be captured.  The presence of strong neutron absorbers like Chlorine have a capture cross section about 100 times that of Hydrogen at the thermal level.  Thermal neutrons therefore need to be corrected for fluid salinity and matrix capture cross section effects.  Epithermal neutrons do not need to be corrected for capture effects but only have one tenth of the population of thermal neutrons.  Some neutron tools like the CNT-GA can detect both epithermal and thermal neutrons giving two different porosity measurements.  The standard CNT Tool measures only thermal neutrons.
  • 53. NEUTRON LOG APPLICATION  The Neutron tool is used to determine primary formation porosity, often called the pore space on the formation rock which is filled with water, oil or gas.  Together with other tools like the density, the lithology and formation fluid type can also be determined.
  • 55. NEUTRON LOG Presentation  Presented in track 5 and 6 by a dashed line with the mnemonic NPHI and with scales, 45% to –15% (or .45 to –0.15 p.u.-porosity units Typical Log Readings 100% Limestone = 0% 100% Sandstone = -2% 100% Dolomite = 1% Shale = 30-45%
  • 58. DENSITY LOG THEORY OF MEASUREMENT  A 1.5 Ci Cs137 chemical source bombards gamma rays at 662keV energy into the formation.  The high-energy gamma rays interact with the electrons of the formation by way of Compton scattering and lose energy in the process.  Other processes also occur namely photoelectric absorption and pair production, although pair production only becomes significant at energies above 1MeV.  A low number of gamma rays detected through Compton scattering will indicate a high electron density.  A spectral or litho density tool measures not only the bulk density but also a photoelectric absorption index PEF.
  • 59. DENSITY LOG  The photoelectric effect occurs when the incident gamma ray of low energy is absorbed by the electron and the electron is then ejected from the atom. PEF = (Z/A)3.6 A=Atomic weight, Z=Atomic number (or # of hydrogen atoms)  The photoelectric effect of absorbed gamma rays is directly related to the Z, the number of electrons per atom, which is fixed for each element.  Different values of the PE curve indicate different types of formation rock being measured and are independent of formation porosity.
  • 61. DENSITY LOG APPLICATION  The density tool is used to determine formation density and estimate formation porosity.  Together with other tools like the Neutron, the lithology and formation fluid type can also be determined.  The density tool can distinguish between oil and gas in the pore space by virtue of their different densities.  Modern density tools also measure the photoelectric effect to help distinguish between rock lithologies, recognize presence of heavy minerals, fracture identification when barite is present and additional clay evaluation.  In addition the density can be used to determine Vclay and to calculate reflection coefficients to process synthetics.
  • 63. DENSITY LOG Synthetic Processing  The Density is used along with the Sonic velocity to compute Acoustic impedance (I) by:- I = Density(rho) * Velocity (V)  The Reflection coefficient (R) at a bed boundary is then determined by:- R = (I2 - I1) / (I2 + I1)  The Reflection coefficient is then used to generate synthetic processing curves that can match the exploration seismic
  • 64. DENSITY LOG PRESENTATION  Presented in track 5 and 6 by a thin continuous line with the mnemonic RHOB.  For sandstone scales, 1.90 to 2.90 with units of g/cc and neutron from 45% to – 15%.  For limestone scales, 1.95 to 2.95 with units of g/cc and neutron from 45% to – 15%.  The amount of density correction is presented in track 6 by a dashed line with the mnemonic DRHO.  DRHO scales are -0.25 to 0.25 with units of g/cc.
  • 66. DENSITY LOG Using compatible limestone scales for density (1.95 RHOB 2.95) and neutron curves (45% NPHI –15%) then:-  In a clean wet limestone RHOB and NPHI curves will overlay.  In a shale RHOB plots right of NPHI depending on the amount of shale present.  In a gas limestone RHOB plots > 3pu left of NPHI  In a clean wet sand RHOB plots 3pu left of NPHI  In a dolomite RHOB plots right of NPHI Using compatible sandstone scales for density (1.90 RHOB 2.90) and neutron curves (45% NPHI –15%) then:-  In a clean wet sand RHOB and NPHI curves will overlay.  In a shale RHOB plots right of NPHI depending on the amount of shale present.  In an oil sand RHOB plots 1-3pu left of NPHI  In a gas sand RHOB plots > 3pu left of NPHI
  • 67. DENSITY LOG Mineral RHOB (g/cc) PEF 100% Limestone 2.71 5.09 100% Sandstone 2.65 1.81 100% Dolomite 2.85 3.05 Shale 2.2-2.7 3.36 (typically) Anhydrite 2.92-2.98 5.05 Salt 2.06 4.65 Coal 1.68 0.18 Hydrogen -0.61 Carbon -0.29 Water 1 -0.02 Typical Log Readings
  • 69. SONIC LOG THEORY OF MEASUREMENT:  Transmitter emits sound waves into the formation and measures the time taken to detect at a receiver of known distance from the transmitter.  The Sonic tool operates at 20 cycles per second as sounds similar to a pedestrian crossing at a set of traffic lights.  The first arrival is the compressional or 'p' waves, which travel adjacent to the borehole  It is this arrival that is used to measure the individual travel times T1, T2, T3, and T4. Two receivers for each transmitter eliminates the borehole signal.  The transit time DT is computed from these travel times as shown in the equation below.  This particular arrangement of sonic tool transmitters and receivers is known as the standard BHC Sonic tool and compensates for borehole washouts and also for tool tilting in real time while logging. DTLOG = [(T1 - T2) + (T3 - T4)] / 2
  • 70. SONIC LOG  T1 and T3 travel times have a Tx-Rx spacing of 5 feet and T2 and T4 travel times have a Tx-Rx spacing of 3 feet.  This results in a DT of 2 feet and is also the vertical resolution of the tool. The shear signal arrives next which usually has a slightly larger amplitude than the compressional arrival, then mud arrivals and Stoneley waves.  The various arrivals in the received sonic signal can be seen in Figure 1. Stoneley waves are used to interpret the existence of fractures
  • 72. SONIC LOG APPLICATION: • Porosity PHIS • Volume of clay VS • Lithology • Time-depth relationship • Reflection coefficients • Mechanical properties • VDL/CBL  By combining sonic and Checkshot data we can calibrate down hole log data with surface seismic data.  Mechanical properties can be determined from the shear and compressional waves, fracture identification from shear and Stoneley waves and permeability indication from Stoneley waves Presentation  Presentation is usually 140-40 us/ft (or 500-100 us/m) across tracks 5 & 6
  • 74. SONIC LOG . Material Delta-T(us/ft) Non Porous Anhydrite 50 Solids Calcite 49.7 . Dolomite 43.5 . Granite 50.7 . Gypsum 52.6 . Limestone 47.6 . Quartz 52.9 . Salt 66.6 . Steel 50 . Casing 57.0 Water Saturated Dolomites (5-20%) 50.0-66.6 Porous Rocks Limestone (5-20%) 54.0 - 76.9 . Sandstones (5-20%) 62.5 - 86.9 . Sands (unconsolidated - 20- 35%) 86.9 - 111.1 . Shales 58.8 - 143.0 Liquids Water (pure) 208 . Water (100,000mg/L of NaCl) 192.3 . Water (200,000mg/L of NaCl) 181.8 . Petroleum 238.1 . Mud 189 Gases Hydrogen 235.3 . Methane 666.6
  • 76. RESISTIVITY LOGS THEORY OF MEASUREMENT  Most resistivity logs measure from 10 to 100 ft3 of material around the sonde, however the micro-resistivity log measures only a few cubic inches of material near the borehole wall.  Resistance (R-Ohms) is related to current (I-Amps) and voltage (V-Volts) according to Ohm’s law and is described by: - V= IR  Resistivity (R) can be defined as the property of a material that resists the flow of electric current, and is the voltage required to pass one amp through a cube with a one meter square face area.  The unit of measurement is Ohm-meter2/meter (ohm m2/m or ohm m).
  • 77. RESISTIVITY LOGS  The Induction logging tool determines resistivity by measuring the formation conductivity.  The Induction tool induces and focuses an electromagnetic field into the formation adjacent to the tool by generating an alternating current source in the primary coil.  This induced electromagnetic field will produce a measurable current and potential in the receiver coil of the tool proportional to the formation conductivity.  The primary and secondary windings of a common transformer are a simple analogy.  The measured voltage in the receiver coil is then used to determine the formation conductivity and thus the formation resistivity.  Conductivity is the inverse of resistivity (1/resistivity) and has the units of mho/m
  • 78. RESISTIVITY - REVIEW 1 Volt 1 meter - + Resistivity 1 W-m2/m
  • 81. INDUCTION PRINCIPLES Alternating Signal, I(wt) ~ Transmitter Oscillating Transmitted Magnetic Field, B(wt) Induced Formation Current J(wt) ≈ aE(wt) Detected Magnetic Field, B2(wt) Received Signal, I2(wt) Receiver Secondary Magnetic Field (from induced formation currents)
  • 82. WHEN TO RUN INDUCTION High Water Resistivity, Rw Medium Water Resistivity, Rw Low Water Resistivity, Rw High Mud Resistivity, Rm Normally OK for induction logs, if porosity > 8% otherwise Rt may be too high (over 250 W- m) Perfect for induction logging. Perfect for induction logging. Medium Mud Resistivity, Rm Normally OK for induction logs if porosity > 10% Perfect for induction logging. Perfect for induction logging. Low Mud Resistivity, Rm Not advised. Borehole signal will often be larger than formation signal Acceptable for induction logging if porosity > 6% and hole diameter < 10 inches, otherwise borehole signal may overwhelm formation signal
  • 84.
  • 85. PETROPHYSICAL ANALYSIS STEP 1: VOLUME OF SHALE: 1) From Gamma Ray Log: Vshale_IGR = (GRlog-GRminimum) / (GRmaximum-GRminimum) 2) From SP Log: Vshale_ISP = (SP-SPcln) / (SPshl-SPcln) Clavier Shale Correction Vshale= 1.7 - (3.38 - (Vshale_IGR+0.7)^2)^0.5 Steiber Shale Correction Vshale = 0.5 * Vshale_IGR / (1.5 – Vshale_IGR)
  • 86. PETROPHYSICAL ANALYSIS STEP 2 Net To Gross Ratio (NTG): NTG=1-Vshale
  • 87. PETROPHYSICAL ANALYSIS STEP 3: Befrore moving to this step first of all we have to identify lithology , if we don’t have the well tops, the formula used for that purpose is . RHOMa = (RHOB - PHIA * RhoF) / (1 - PHIA) Step 3 involves the calculation of porosity Different porosity types which are estimated from well logs are as follows 1) Density porosity 2) Neutron porosity 3) Average porosity 4) Sonic porosity 5) Effective porosity
  • 88. PETROPHYSICAL ANALYSIS STEP 3.a. DENSITY POROSITY: DPHI = (RhoM - RHOB) / (RhoM - RhoF) RhoM= density of matrix (constant values) RhoF= density of fluid (on log header) RHOB= Bulk Density ( density log values) Sandstone 2.65 Limestone 2.71 Dolomite 2.87 Fresh Water 1.0 Salt Water (120kppm) 1.1 Oil 0.85
  • 89. PETROPHYSICAL ANALYSIS STEP 3.b: Sonic porosity: Øsonic = (∆tlog - ∆tma) / (∆tf -∆tma) Øsonic = Sonic derived porosity ∆tma = Interval transit time of the matrix ∆tlog = Interval transit time of formation ∆tf = Interval transit time of the fluid in the well bore (Fresh mud = 189; salt mud = 185)
  • 90. PETROPHYSICAL ANALYSIS Where a sonic log is used to determine porosity in unconsolidated sands, an empirical compaction factor or Cp should be added to the Wyllie et al equation: Øsonic= (1/Cp) x [(∆tlog - ∆tma) / (∆tf -∆tma)] Øsonic = Sonic derived porosity ∆tma = Interval transit time of the matrix ∆tlog = Interval transit time of formation ∆tf = Interval transit time of the fluid in the well bore (Fresh mud = 189; salt mud = 185) Cp = Compaction factor Cp = (∆tsh x C ) /100 ∆tsh = Interval transit time for adjacent shale C = Constant which is normally 1.0 Empirical corrections for hydrocarbon effect: Øsonic x 0.7 (gas) Øsonic x 0.9 (oil)
  • 91. PETROPHYSICAL ANALYSIS Lithology ∆tma(µsec/ft) commonly used Sandstone 55.5 to 51.0 Limestone 47.6 Dolomite 43.5 Anhydrite 50.0 Salt 67.0 Shale 167.5 - 62
  • 92. PETROPHYSICAL ANALYSIS STEP 3.c: Average Porosity: Also called as Neutron-Density Porosity, Neutron-Sonic Porosity as well ØN-D= √(ØN 2+ ØD 2/2) Whenever N-D Porosity log records density porosity of less than 0.0, a common value is anhydrite. The following formula should be used to determine the N-D porosity: ØN-D= (ØN 2+ ØD 2/2)
  • 93. PETROPHYSICAL ANALYSIS STEP 3.d: Effective Porosity: Effective porosity=NTG*Average Porosity
  • 94. PETROPHYSICAL ANALYSIS STEP 4: Resistivity of Water (Rw): To calculate Rw there are several methods some of which invlove the usage of standard sclumberger plots, while there are other in which we use certain standard equations. All steps with equations are explained as follows with their sub steps as wells
  • 95. PETROPHYSICAL ANALYSIS STEP 4.a: Rmf at 75°F=Rmf*(temp+6.77)/81.77 STEP 4.b: K=60+(0.133*Tf) Tf=Formation Temperature To calculate formation temperature we have to perform following steps TEMPERATURE GRADIENT CALCULATION: m=y-c/x y=bottom hole temperature(BHT) X=total depth of well C=surface temperature FORMATION TEMPERATURE CALCULATION: Tf=m*x+c Here x= Formation Depth
  • 96. PETROPHYSICAL ANALYSIS STEP 4.c: Rmfe/Rwe=10^(-SSP/K) Rmfe/Rwe=Ratio of resisitivity of mud filtrate equvalent to resistivity of water equivalent K= from step 4.b. SSP= static spontaneous potential CALCULATION OF SSP:  First take SP in shale zone (Zone where GR is high representative of thick shale package)—Shale baseline  Then note SP in clean zone (porous, where hole condition is OK, don’t go for Overguaged zones)__Sand baseline Example: SPshale= -20mV SPsand= -30mV SSP=-10mV SPshale= -30 SPsand= -20 SSp=+10mv
  • 97. PETROPHYSICAL ANALYSIS STEP 4.d: if Rmf at 75°F<0.1 then use following formula Rmfe=(146*Rmf-5)/(337*Rmf+77) If Rmf at 75°F>0.1 then use following formula Rmfe=0.85*Rmf STEP 4.e: Rwe=Rmfe/(Rmfe/Rwe) Rwe=Resistivity of water equivalent Rmfe= from step 4.d Rmfe/Rwe= from step 4.c
  • 98. PETROPHYSICAL ANALYSIS STEP 4.f: If Rwe <0.12 use following formula Rw @ 75°F=(77*Rwe+5)/(146-377*Rwe) If Rwe >0.12 use following formula Rw @ 75°F =-[0.58-10^(0.69*Rwe-0.24) ] STEP 4.g: Rw @ formation temperature=(Rw @ 75°F *81.77)/(Tf+6.77)
  • 99. PETROPHYSICAL ANALYSIS 99 BTC STEP 5: Calculation Of Sw: lateral log deep (LLD) F=a/Ø m induction log deep a=1 m=2 n=2
  • 100. PETROPHYSICAL ANALYSIS STEP 6: Calculation Of Sxo: Induction Log Shallow STEP 7: micro spherical focused log Calculation of Moveable Hydrocarbons given on the log header STEP 8: Calculation of Bulk volume of water(BVW):
  • 101. PETROPHYSICAL ANALYSIS STEP 9: Calculation of Bulk volume of Hydrocarbon or Hydrocarbon Pore Volume(HCPV): HCPV=Ø (1- Sw) STEP 10: Calculation of residual oil saturation: ROS= 1 - Sxo STEP 11: Calculation of moveable oil saturation: MOS= Sxo - Sw
  • 102. PETROPHYSICAL ANALYSIS STEP 12: Calculation of Permeability: Swirr=Saturation of water (irreducible) Swirr= [a/(2000*NPHI m )] 0.5
  • 103. PETROPHYSICAL ANALYSIS STEP 13: Reserves Calculation: Oil in Barrels; Depth in Feet BBL = 7758 * Acres * PHIA * (1 - Sw)*h*R.F*Shape factor Gas in Mcfd; Depth in Feet MCF = 43,560 * Acres * PHIA * (1 - Sw)*h*R.F*Shape factor R.F=60-80% (gas), 20-30%(oil)